7
HOW VICTORIA'S LONG OUTFALLS WORK

[ed note: The diagram mentioned below is not yet available online.]

The diagram at the centrefold of this book shows the location of the
Macauley Point and Clover Point outfalls and a cross section at the
points of discharge. It has been distorted to simplify explanations
but that does not invalidate the principle that it illustrates. In
reality the rising column of sewage is much
narrower in relation to its height than the diagram indicates;
also it will be skewed to one side or the other depending on the
currents.

It will be seen that the sewage discharges a little under a mile from
shore in the one case and a little over a mile in the other
at a depth of about 200 feet, which is greater than Victoria's
tallest buildings. The force that drives the column upwards is
the temperature and salinity difference between the sewage and
the surrounding sea. The extreme cold in the Straits year round
ensures that the column pours upwards rapidly. As it does so it
entrains sea water so the column becomes closer and closer to the
composition of the sea as it rises. Before this driving force
has expended itself the column is only one half of one percent
sewage, at the most, and is commonly one tenth of one percent.
These figures may be compared with the effluent discharging from
a secondary treatment plant which will usually be at ten percent
of the incoming sewage strength. Indeed, a sample taken a little
way up the vertical column will already be superior to such an
effluent. Furthermore a discharge of secondary treated effluent
through a short outfall would be worse than the raw sewage
discharging down the long outfalls.

The column may be thought of as a vertical tank, bounded by the laws
of physics as effectively as a land-based treatment tank is bounded by
concrete but bigger, more efficient, requiring
no power and not subject to any form of failure.

The hugely diluted mass then disperses horizontally, rapidly
reaching a state that is indistinguishable from sea water, even
under the most acute tests. Such a test is the 'coliform' test,
already mentioned, which can detect coliforms at less than one
millionth of the strength of the incoming sewage. No test has
yet revealed coliforms along our shorelines from the long
outfalls, although there are plenty of coliforms from other
discharges.

This state of affairs may be compared with the discharge of
secondary treated effluent to a stream or river, which is a
perfectly acceptable practice. The effluent, effectively diluted
ten fold as explained, will there discharge to the watercourse
which will dilute it further, depending on the ratio of the river
water to the amount of effluent.

In the one case a liquid mass one two hundredth to one
thousandths of the strength of sewage discharges one mile from
shore into salt water. In the other a liquid mass one tenth of
the strength of sewage discharges to fresh water, which pathogens much
prefer, some feet from the adjoining banks. Commonly there will be
property near the river some little way downstream. There are numerous
such discharges doing no harm to the environment nor to man. How can
our sea discharges be doing harm?